Tandem wheel arrangements have two or more wheels arranged in line with each other. Earthmoving machines, for example, use tandem wheel arrangements for applications requiring traction and stability while operating over rough terrain. One such machine, for example, is a motor grader, which is a type of machine that is typically used to create a flat or graded surface on a landscape. Other examples of machines or vehicles having tandem drive arrangements include trucks, trains, moving platforms, gantry cranes, military vehicles, and so forth. Tandem wheel arrangements may employ hydraulic, electrical, or mechanical power to propel one or more of the wheels in the arrangement.
A typical drive configuration for tandem wheels includes a rotating input sprocket that powers one or more wheels of the arrangement via chains. The sprocket, chains, and associated gears are typically enclosed within an enclosure or beam, which is pivotally connected to the machine on the centerline of the sprocket. The chains are arranged to provide torque to each driven wheel and the input torque to the sprocket must equal the sum of the output torques to the wheels, otherwise, a moment may be applied to the tandem drive arrangement. This moment may cause instabilities, for example, by lifting a portion of the tandem wheel arrangement relative to another portion such that one or more wheels of the arrangement cannot fully engage the driving surface. A common application of tandem wheel arrangements include two wheels. Such arrangements typically have both wheels capable of powered rotation, preferably at equal torques, such that the tandem arrangement remains balanced and stable.
One example of a known drive torque balancing system can be seen in U.S. Pat. No. 3,786,888 (the '888 patent), which issued on Jan. 22, 1974. The '888 patent discloses a vehicular walking beam suspension system, which provides equal ground pressure under dynamic conditions. The drive system disclosed includes a gear reduction arrangement provided at each wheel hub that generates torque reactions at the wheels. These torque reactions are transferred directly and continuously back to the chassis of the vehicle via a system of beams and linkages.
One disadvantage of the drive system disclosed in the '888 patent is the relative complexity with which the various components of the drive arrangement are assembled. More particularly, the function of the linkages that equalize torques across the driven beam require that two different sets of bearings are disposed between the beam, the wheel hub, and the ring gear of the planetary gear system that is driving each of the wheels. The relatively high number of bearings (eight on either side of the vehicle for a total of sixteen) makes this arrangement less reliable and more prone to failure when subjected to severe service conditions in the field.